In using the nonhuman primate as an auditory model for man we hope to obtain a more precise understanding of the nature of hearing loss due to intense sound and noise and ototoxic drugs. We hope, for example, to be able to specify the conditions which produce broad band versus frequency specific hearing loss, either reversible or permanent in nature. We plan to examine more thoroughly the cumulative effects of both drugs and noise. Particularly important is the relation between hearing impairment and cochlear histopathology; in an attempt to clarify this relationship we have continued working with Dr. J.E. Hawkins, jr. Behavioral conditioning methods, together with audiometric testing procedures (i.e. Bekesy audiometry) are used for threshold testing, for frequency and intensity difference thresholds, and for assessment of the discrimination of loudness levels. Monkeys with a clearly established hearing loss as a consequence of exposure to intense sound or drug treatment are sacrificed and histological changes in the cochlea are compared with the final audiometric results.